Bone voids and non-unions are often the result of trauma, fracture, tumor removal, or surgical implant procedures such as total joint replacement. Bone voids and non-unions are treated in a variety of ways. In many cases, surgeons take filler and apply it at the site of the bone void or non-union to fill in gaps and help the bone grow. This filler may be or include constituents from the patient's own body, a donor's body, or another species' body, as well as other naturally occurring and synthetic substances. The filler is typically a mixture of a clotting agent with blood platelets and/or bone graft. Some people believe that blood platelets facilitate the healing of bone and other tissue and that bone graft and similar substances provide useful scaffolding for new bone to grow around.
In some surgical procedures, blood is taken from the patient and used to create a platelet rich concentration by separating out the platelets from other components of the blood. The platelet rich concentrate is then mixed with one or more clotting agents, such as thrombin, collagen (e.g. gelfoam, microfibrillar collagen), calcium salts (e.g. calcium chloride), gelatin paste or foam, fibrin glue, bone wax, epinephrine, and/or oxidized cellulose, which facilitate congealing. Thrombin, for example, breaks down some of the blood components and causes them to interdigitate or weave themselves together. After a short period of time, the mixture congeals and may be used to treat a bone fracture, a non-union area, or a bone void. The presence of blood platelets may help the patient heal or heal faster then he or she otherwise would. The area filled in may eventually turn back into bone. Note that the use of the platelet rich mixture is not limited to filling bones. Such mixtures are thought to have healing benefits for other tissue types as well. For example, a tissue wound such as a burn may benefit from treatment with a platelet rich mixture. The mixture may be applied to help the skin reform. A variety of other uses are possible.
In the case of bone voids and non-unions, the filler may contain a scaffolding substance, such as bone graft, that provides a scaffold for new bone to grow around. Bone graft is morcelized or crumbled up bone and may come from a donor (allogenic), the patient's own bones (autologous), or from another species' bones (xenologous). In addition to naturally derived bone graft, a synthetic substance such as a resorbable polymer may be used as a scaffolding substance. Ceramics such as calcium phosphate, calcium sulfate, or silicon oxide may be used. The scaffolding substances may be any combination of osteoconductive, osteoinductive, or biocompatible materials.
Generally, a filler mixture is composed of a clotting agent and one or more of blood, blood derived product, bone marrow, or bone marrow derived product. Thus, for example, filler may be a mixture of a clotting agent, a scaffolding substance, and a platelet rich concentrate. Such filler might be used in a bone graft procedure in which the filler is inserted into a bone void to provide an environment for and induce new bone growth. The mixture may include a variety of other inputs like proteins, angiogenic factors, osteogenic factors, antibacterial agents, drugs, pain medication, and/or any other suitable medically beneficial input.
The mixture of clotting agent with other input constituents or materials is often performed at or around the time of the surgical procedure in which the mixture is used. In some cases, this is because the use-ability and ease of handling of the congealed mixture begins to decrease after the mixture has congealed for an hour or so, when it begins to shrink and secrete liquid. For a relatively short period of time after congealing, the mixture is typically easier to handle because it can be easily cut and shaped. After congealing for five hours, many mixtures will have become unusable. In addition, when inputs from the mixture come from the patient (e.g., blood platelets), it is often convenient to obtain those inputs from the patient at or around the time of surgery rather than long before. Generally, within a minute or a minute and a half of mixing, the mixture congeals into a useable substance that is good for up to around five hours.
There are a variety of ways to mix the clotting agent with the other input or inputs. For example, the surgeon may make the mixture by adding the ingredients to a small dish or bowl and mixing them. As another example, the materials may be placed together into a syringe as in U.S. patent application 2002/0127720 to Erbe et al., which is incorporated herein by this reference. Erbe et al. describe a syringe for bone marrow aspirate and other biocompatible materials in which mixing can occur. However, there is potential for the constituents not to mix as desired.
Similarly, there is, among other things, potential for the constituents to not interact as desired in the Depuy Symphony Graft Delivery System, which allows two liquids to enter a conveyance device where they interact. The end user may or may not be successful at facilitating sufficient interaction and mixing with manual agitations such as by shaking the container. U.S. Patent Publication No. 2004/0167617 to Voellmicke et al., which is incorporated herein by this reference, describes an apparatus for mixing and retaining biological fluids. A manifold is used to deliver materials from two or more input syringes into a fluid retention chamber. However, an object of the Voellmicke et al. invention is “to provide a apparatus for mixing and retaining biological fluids comprising a manifold which minimizes intra-manifold mixing of the fluids.” The manifolds do not facilitate, and in many cases minimize, intra-manifold mixing. There is again, among other things, the potential that the inputs will fail to mix or interact sufficiently.